In optical systems, it is desirable to generate light with good spectral purity, broad wavelength range, and saturation (control of illumination intensity) using a minimum amount of power and having a compact size. Many current technologies are available, such as incandescent, arc-discharge, light emitting diodes, and lasers. However, each of these technologies suffers in that they are incompatible with at least one of the desirable properties listed above.
Incandescent sources having wavelength filters have been used for generating a broad range of wavelengths with good spectral purity. Notwithstanding, these incandescent sources are undesirable in that they consume relatively large amounts of power and generate a substantial amount of heat. Also, control of saturation at a particular wavelength is difficult because when an incandescent source is dimmed, the amount of blue light generated decreases relative to the red light generated. The opposite effect occurs when the brightness of an incandescent source increases. An incandescent source is often driven at a constant temperature and light modulators are used to achieve the desired intensity control, otherwise known as saturation or gray level. Although the incandescent light source with a modulator works in many applications, there is an undesirable bulk and complexity associated with the combination of the light source and the modulator when used in a product. Furthermore, there is a need to dissipate a large amount of heat generated from an incandescent source. Dissipating a large amount of heat makes a compact source unfeasible, which limits usefulness of this incandescent source.
Arc-discharge sources consume less power than incandescent sources, however the problem of heat dissipation still remains. Therefore, there is a limit to broad product application of an arc-discharge source. The arc-discharge source suffers from all the aforementioned problems of an incandescent source, except the power consumption is less. Also, since the power spectrum of an arc-discharge source is not uniform, many desired wavelengths may not be generated. Furthermore, the arc-discharge source requires a high voltage to strike the arc. This high voltage requirement adds further complexity and bulkiness. Therefore, it is unlikely that a compact source will use an arc-discharge source.
Light emitting diodes have good spectral purity, relatively easy control of saturation, low power consumption, and a compact size. However, the wavelength of emitted light is fixed and not broadly adjustable. The fixed wavelength occurs because the output of each individual light emitting diode is determined by the material used to make the light emitting diode. Since wavelength is specific to a particular material, it cannot be used to produce light over a broad range of wavelengths. Therefore an individual light emitting diode cannot support a broad range of wavelengths.
Lasers have very good spectral purity and an extremely high radiance (energy per area per solid angle) which is unattainable by other light sources. However, a tunable laser having a broad wavelength range, good saturation control and compact size has yet to been developed.
In order to enable a broad range of product applications, an optical source having the desirable optical properties of good spectral purity, tunability over a broad wavelength range, good control of saturation, and/or compact size would be useful. This optical source may, for example, enable applications in: Display technologies such as personal projectors and near eye displays; health and wellness testing systems based on optical techniques such as spectrum analysis of assays; home and commercial offices such as printers for printing and imaging of documents and pictures; optical network and communication systems such as modulators. Furthermore, each of these applications can be made portable by using a compact source of light with the above mentioned properties.
Therefore, there is a need for a compact optical source having good spectral purity, tunability, and/or control of saturation.